1. Technical Field
This invention relates to communications networks, and more particularly to a method for monitoring a network to generate topology information.
2. Description of the Related Art
An operator needs management information about a network to help conceptualize the network and call attention to adverse changes in a fast and accurate manner. A network could be a collection of voice, video, or data processing devices connected by communication lines. As the network complexity increases, it becomes more difficult to conceptualize how various pieces are laid out. One way to help the operator visualize the layout is to display a topology map showing each node and the connections which exist between the nodes. One system accomplishing this visual display is described using virtual-world technology to provide 3-D input and output capabilities to facilitate management tasks; this system is described by L. Crutcher et al, "Management and control for Giant Gigabit Networks," IEEE Commun. Mag., Vol. 7, No. 6, pp. 62-71, November 1993.
The topology map needs to reflect the actual network topology and its current status in real-time, as accurately as possible, so an operator can respond quickly to possible network trouble spots. This need is most evident in broadband networks where an outage would impact many end-to-end connections. In addition, each connection may suffer large amounts of information loss before the source can be suspended or an alternate path can be established to re-route traffic.
To build and continuously update the topology map, information must be collected from each network node. The challenge is to do this in real time without adversely consuming network bandwidth. The simple polling approach to gather network information has severe problems in wasting network bandwidth, as described in Rose, "The Simple Book," p. 76, Englewood Cliffs, N.J.: Printice Hall Inc. This is of special concern in wide-area networks where recurring transmission line expenses directly affect the cost of network operation. Bandwidth used by management traffic comes at the expense of user bandwidth. Even in broadband networks, such as ATM networks, minimizing management bandwidth usage is a concern. A requirement for one standard (ATM forum's requirement for ILMI) is that management traffic be less than one-percent of line capacity. Since topology monitoring is but one part of the overall management function, it is necessary to minimize traffic generated by the topology application.
In the system of this invention, topology management monitors point-to-point networks in which each node only contains information concerning its neighboring nodes. This simplifies the node's implementation and thus reduces its cost. Existing monitoring systems for point-to-point networks utilize either polling or event-monitoring modes, as will be described.
In a point-to-point network, typically seen in a WAN, one link or trunk directly connects two network nodes, and this trunk connection established between two nodes is not shared with other nodes. Due to transmission line costs, each node has a relatively small number of trunk connections. In some point-to-point network architectures, each node maintains an updated copy of the entire network topology. Therefore network topology monitoring can be performed by collecting information form only one network node, or two to verify the integrity of the information. One example is a feature of an IBM system called APPN Topology and Accounting, described in APPNTAM Feature Implementation Guide, Version 2 Release 4, pp. 2,85, January 1994. The APPNTAM employs event monitoring, but unlike this invention, requires each network node to have a full topology.